Micro through-silicon via for transistor density scaling

ABSTRACT

An electronic device comprises an integrated circuit (IC) die. The IC die includes a first bonding pad surface and a first backside surface opposite the first bonding pad surface; a first active device layer arranged between the first bonding pad surface and the first backside surface; and at least one stacked through silicon via (TSV) disposed between the first backside surface and the first bonding pad surface, wherein the at least one stacked TSV includes a first buried silicon via (BSV) portion having a first width and a second BSV portion having a second width smaller than the first width, and wherein the first BSV portion extends to the first backside surface and the second BSV portion extends to the first active device layer.

PRIORITY APPLICATION

This application claims the benefit of priority to Malaysian ApplicationSerial Number PI 2018702670, filed Jul. 31, 2018, which is incorporatedherein by reference in its entirety.

TECHNICAL FIELD

Embodiments pertain to packaging of integrated circuits (ICs). Someembodiments relate to IC package interconnection of integrated circuits.

BACKGROUND

Electronic systems often include integrated circuits (ICs) that areconnected to a subassembly such as a substrate or motherboard. Aselectronic system designs become more complex, it is a challenge toroute the desired interconnection of the ICs of the systems. One aspectthat influences the overall size of a design is the size and spacingrequired for the interconnection of the ICs. As the spacing is reducedto meet performance goals, the electronic system can become less robust.Thus, there are general needs for devices, systems and methods thataddress the spacing challenges for routing of system interconnection yetprovide a robust and cost effective design.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of a three-dimensional (3D) integrated circuit(IC) package in accordance with some embodiments;

FIGS. 2A and 2B are blowup illustrations of a portion of the base IC dieof FIG. 1 including a stacked through silicon via (TSV) in accordancewith some embodiments;

FIG. 3 is an illustration of another 3D IC package in accordance withsome embodiments;

FIG. 4 is a blowup illustration of portions of the base IC die andsecond IC die of FIG. 3 in accordance with some embodiments;

FIG. 5 is an illustration of a stacked TSV in accordance with someembodiments;

FIGS. 6A-6I is a flow diagram of a method of forming an electronicdevice in accordance with some embodiments;

FIG. 7 illustrates a system level diagram in accordance with someembodiments.

DETAILED DESCRIPTION

The following description and the drawings sufficiently illustratespecific embodiments to enable those skilled in the art to practicethem. Other embodiments may incorporate structural, logical, electrical,process, and other changes. Portions and features of some embodimentsmay be included in, or substituted for, those of other embodiments.Embodiments set forth in the claims encompass all available equivalentsof those claims.

To meet the demand for increased functional complexity in smallerdevices, through-silicon vias (TSVs) can be used to route signalinterconnect vertically in IC die. However, current manufacturingprocesses for TSVs require a large keep-out-region (KOR) to provideclearance between the TSVs and transistor devices in silicon substrates.The KOR is necessary to prevent transistor functionality breakdown dueto thermo-mechanical stress. The KOR requirement for TSVs can besignificant and can reduce the total area available for transistorplacement in an IC. This can impose undesirable constraints ontransistor density scaling, but reducing the KOR can poses risks oftransistor performance degradation due to the undesirable mechanicalstress. This is particularly more pronounced if the TSVs arecopper-based because copper has a significantly different coefficient ofthermal expansion (CTE) compared to silicon.

FIG. 1 is an illustration of a three-dimensional (3D) IC package 100.The IC package includes a multi-layer package substrate 102. The ICpackage includes solder balls 104, one or more passive electroniccomponents 106 (e.g., capacitors), a first or base IC die 108, and asecond IC die 110. The IC dies can include, among other things, one ormore of a central processor unit (CPU), a platform controller hub (PCH)chipset, dynamic random access memory (DRAM), and a field programmablegate array (FPGA).

The base IC die 108 includes a bonding pad surface 112 and a backsidesurface 114 opposite the bonding pad surface 112. The backside surface114 may have been the backside of a silicon wafer before the fabricatedICs were separated into die. The backside surface 114 includes packagesolder bumps 118 for coupling to the multi-layer package substrate 102and providing continuity to the interconnect between the multi-layerpackage substrate 102 and the base IC die 108. The bonding pad surfaceincludes micro solder bumps 120 for coupling the IC die and forproviding continuity to the interconnect between the IC die. The base ICdie 108 also includes multiple stacked TSVs 122.

FIGS. 2A and 2B are blowup illustrations of a portion of the base IC die108 of FIG. 1 including a stacked TSV. The stacked TSV includes a firstburied silicon via (BSV) portion 224 and a second BSV portion 226. Thetwo BSVs combine to form the stacked TSV. The stacked TSV extendsbetween the backside surface 214 and the bonding pad surface 212 of theIC die. In the example of FIGS. 2A and 2B, the first BSV portion 224extends to the first backside surface 214.

FIGS. 2A and 2B also show an active device layer 228 that includestransistor devices 230. The second BSV portion 226 has a width smallerthan the width of the first BSV portion 224. KOR 232 separates thesecond BSV portion 226 and the active device layer 228. Because thesecond BSV portion has a smaller width, more active devices (e.g.,transistors) can be fabricated in the active device layer than if thestacked TSV had a uniform width of the first BSV portion 224.

The multi-width solution shown in FIGS. 2A and 2B is more desirable thanmerely making the entire stacked TSV with the smaller width. An ICmanufacturing process typically places an aspect ratio threshold of TSVwidth and height (e.g., width:height aspect ratio of 1:10) in order toreliably fabricate TSVs. Uniformly reducing the width also reduces theheight, which limits the thickness of the IC substrate in order for theTSV to reach the desired locations in the IC. Limiting the thickness ofthe silicon substrate increases the challenges of silicon substratewarpage and thermal dissipation in the ICs. The multi-width solutionrelaxes the aspect ratio limit compared to the uniformly thinner TSVsolution.

FIGS. 2A and 2B further show a stack of metal and via layers 246disposed above the active device layer 228. The Figures includerepresentations for metal layers M0-M14, giant metal layers GM0 and GM1,and vias 248. In FIG. 2A, the stacked TSV only extends to the activedevice layer 228. In FIG. 2B, the stacked TSV extends into the metal andvia layers 246 and lands on metal interconnect layer 14 (M14), but thestacked TSV can land on any of the metal layers. The second BSV portion226 can also be in electrical contact with the bonding pad surface 212.In some aspects, the second BSV portion 226 can extend to the bondingpad surface 212 of the IC die. In some aspects, the second BSV portion226 interconnects with a metal layer or bonding pad adjacent the microsolder bump 220. In some aspects, the second BSV portion 226 iselectrically connected to transistors arranged in the active devicelayer 228 through the metal and via layers 246. The width of the firstBSV portion 224 can correspond to a feature pitch size of the backsidesurface 214, and the width of the second BSV portion 226 can correspondto a feature pitch size of the active device layer 228 or the metal andvia layers 246.

Returning to FIG. 1, the second IC die 110 includes a bonding padsurface 134 and a backside surface 136 opposite the bonding pad surface134. The second IC die is arranged on the first IC die with the bondingpad surface 134 of the second IC die facing the bonding pad surface 112of the first IC die. The stacked TSV 122 and micro solder bumps 120 canprovide electrical continuity between the multi-layer substrate 102 andthe bonding pad surface 134 of the second IC die.

The concepts shown in FIGS. 1 and 2 can be extended. FIG. 3 is anillustration of another three-dimensional (3D) IC package 300. The ICpackage 300 includes a package substrate 302, a base IC die 308, asecond IC die 310, and a third IC die 338. The third IC die 338 includesa bonding pad surface 340 that is coupled by solder bumps (e.g., microsolder bumps) to the backside surface 336 of the second IC die.

The base IC die 308 includes at least one stacked TSV 322, and thesecond IC die 310 includes at least one stacked TSV 322 extendingbetween the backside surface 336 and the bonding pad surface 334 of thesecond IC die. The stacked TSVs include a first BSV portion that extendsto the second backside surface and a second BSV portion that has a widthsmaller than a width of the first BSV portion.

FIG. 4 is a blowup illustration of portions of the base IC die 308 andsecond IC die 310 of FIG. 3 including stacked TSVs 422. Each of the TSVsincludes a first BSV portion 424 and second BSV portion 426. The widthof the second BSV portion is less than the width of the first BSVportion, and the second BSV portion extends through an active devicelayer 428 and through metal and via layers 446. The second TSV portionextends to the bonding pads 442 of bonding pad surface 412 and bondingpad surface 434. The bonding pads of the IC dies are coupled by solderbumps 420.

FIG. 5 is an illustration of another stacked TSV 522. A stacked TSV isnot limited to just one change in width size. The stacked TSV 522includes a first BSV portion 524 and a second BSV portion 526. Thestacked TSV 522 includes a third intermediate BSV portion 544 betweenthe first BSV portion 524 and the second BSV portion 526. The width ofthe third BSV portion is smaller than the width of the first BSV portion524 and larger than the width of the second BSV portion 526. In certainaspects, the width of the third BSV portion is nearer to the width ofthe second BSV portion than the width of the first BSV portion. It canbe seen that the stacked TSV 522 includes three BSV portions with twochanges in width size. In some aspects, the stacked TSV includes morethan two changes in width size. In some aspects, the first BSV portion524, the second BSV portion 526, and the third intermediate BSV portion544 comprise similar electrically conductive material. For example, thethree portions may all include one of copper, tungsten, aluminum,silver, gold, tin-silver or tin-silver copper composites. In someaspects, the first BSV portion 524, the second BSV portion 526 and thethird intermediate BSV portion 544 comprise different electricallyconductive material. For example, the first BSV portion 524 may comprisecopper metal, the second BSV portion 526 may comprise tungsten metal,and the third intermediate BSV portion 544 may comprise tin-silvercomposites.

FIGS. 6A-6I is a flow diagram of a method of forming an electronicdevice, such as a 3D IC package for example. FIG. 6A is an illustrationof bulk silicon. The bulk silicon can be a portion of a bulk siliconsubstrate. In FIG. 6B, a first portion of a cavity is formed in the bulksilicon. The first portion can be formed from the backside of a bulksilicon substrate. The first portion can be formed by silicon drilling(e.g., one or more of mechanical drilling, laser drilling, orultra-violet laser drilling), or silicon etching. Because laser drillingtypically evaporates the material being worked it can provide a cleanercavity without material cracking or melting. In some aspects, the depthof the first portion of the cavity ranges from 50% to about 95% of thethickness of the bulk silicon substrate. Preferably, the depth of thefirst portion of the cavity is formed to within 5-10 micrometers (μm) ofthe active device layer. This vertical separation prevents theperformance of transistors or other devices from being adverselyaffected. The first portion of the cavity has a first width. The firstportion of the cavity will be used to form the first BSV portion of astacked TSV. Multiple TSVs may be formed in the bulk silicon, andmultiple cavities may be formed in the bulk silicon for the multipleTSVs.

In FIGS. 6C and 6D, a second portion of the cavity is formed. The secondportion of the cavity has a second width less than the first width ofthe first portion. In FIG. 6C, the second portion of the cavity isformed by a second silicon drilling. In FIG. 6D, the second portion ofthe cavity is formed by a second silicon etching from the other side(e.g., a front side) of the bulk silicon. In some aspects, the depth orheight of the second portion of the cavity ranges from about 5% to 50%of the thickness of the bulk silicon substrate. In some aspects, thesecond portion of the cavity has a separation of 1-10 μm from the activedevice layer in the horizontal direction so that the transistor ordevice performance will not be adversely affected.

In FIG. 6B, the first portion of the cavity can be filled with anelectrically conductive material before the second portion is formed. InFIG. 6E, the second portion of the cavity can be filled with anelectrically conductive material to form a stacked TSV 622. In someaspects, the portions are filled with metal (e.g., copper or aluminum),such as by using a plating process (e.g., an electroless or electrolyticplating process). In the example of FIG. 6E, the stacked TSV includes afirst BSV portion 624 having a first width, and a second BSV portion 626having a second width less than the first width. In certain aspects, thesecond filling process may include a different material than the firstfilling process. For example, the first BSV portion can include copperand the second BSV portion can include tungsten. In some aspects, thefirst cavity portions and the second cavity portion are both formed andthen filled with the electrically conductive material to form thestacked TSV 622. If the first BSV portion and the second BSV portion arefilled individually, one or both of an electroplating process and asolder reflow process can be used to electrically and physically connectthe individual BSV portions.

As explained above, the stacked TSV can include more than two BSVportions. In FIG. 6F, a third portion 644 of the cavity is formed usingsilicon drilling. When filled with the electrically conductive material,the third portion forms a third BSV portion, such as shown in theexample of FIG. 5.

The shape of the BSV portions can be substantially cylindrical and thewidth of a portion can correspond to a diameter. The shape of the BSVportions can be substantially rectangular cuboidal and can be formed asa trench. The shape of the BSV portions can be substantially prismatic.In some aspects, the walls of the BSV portions can be tapered and theshape of the BSV portions can be substantially trapezoidal ortruncated-conical.

In FIG. 6G, an active device layer 628 is formed in a surface of thesilicon substrate opposite the backside surface 614 of the siliconsubstrate. In some aspects, the active device layer 628 is formed afterthe cavity filling of FIG. 6E. A stack of metal and via layers can bedisposed on the active device layer, and a bonding pad surface can bedisposed on the stack of metal and via layers. Because the stacked TSVis formed before the active devices, this can be referred to as aTSV-first fabrication process. In some aspects, the active device layer628 can be formed before the drilling of FIG. 6B. This can be referredto as a TSV-last fabrication process. The stacked TSV can also be formedafter the active device layer 628 and in between formation of the stackof metal and via layers. This can be referred to as a TSV-middlefabrication process. In some aspects, the active device layer 628 can beformed after the cavity filling of FIG. 6E. The stack of metal and vialayers can be disposed on the active device layer, and a bonding padsurface can be disposed on the metal and via layer.

In FIG. 6H, additional silicon substrates are stacked and bonded to thefirst silicon substrate 648. This can be performed at the wafer levelusing a wafer bonding process. A second silicon substrate 650 isarranged on the first silicon substrate 648. The second siliconsubstrate includes a bonding pad surface 634 and a backside surface 636and at least one stacked TSV extending between the backside surface andthe bonding pad surface. The bonding pad surface 634 of the secondsilicon substrate 650 is coupled to the bonding pad surface 612 of thefirst silicon substrate 648. At this point, the bonded wafers can beseparated into stacked IC die.

Instead, of separating the bonded wafers, a third silicon substrate 652can be arranged onto the backside of the second silicon substrate. Thethree bonded wafers can then be separated into assemblies of threestacked IC die.

In FIG. 6I, the backside surface 614 of an IC die of the first siliconsubstrate 648 is coupled to a package substrate 602 using solder bumps.In some aspects, this can include surface mounting of the stacked IC dieand solder reflowing. A mold-underfill (MUF) layer 654 can be applied tothe mounted stacked die using a dispensing or injection process.

An example of an electronic device using assemblies with system levelpackaging as described in the present disclosure is included to show anexample of a higher level device application.

FIG. 7 illustrates a system level diagram, according to one embodimentof the invention. For instance, FIG. 7 depicts an example of anelectronic device (e.g., system) that can include one or more of thestacked TSVs as described in the present disclosure. In one embodiment,system 700 includes, but is not limited to, a desktop computer, a laptopcomputer, a netbook, a tablet, a notebook computer, a personal digitalassistant (PDA), a server, a workstation, a cellular telephone, a mobilecomputing device, a smart phone, an Internet appliance or any other typeof computing device. In some embodiments, system 700 is a system on achip (SOC) system. In one example, two or more systems as shown in FIG.7 may be coupled together using one or more stacked TSVs as described inthe present disclosure.

In one embodiment, processor 710 has one or more processing cores 712and 712N, where N is a positive integer and 712N represents the Nthprocessor core inside processor 710. In one embodiment, system 700includes multiple processors including 710 and 705, where processor 705has logic similar or identical to the logic of processor 710. In someembodiments, processing core 712 includes, but is not limited to,pre-fetch logic to fetch instructions, decode logic to decode theinstructions, execution logic to execute instructions and the like. Insome embodiments, processor 710 has a cache memory 716 to cacheinstructions and/or data for system 700. Cache memory 716 may beorganized into a hierarchal structure including one or more levels ofcache memory.

In some embodiments, processor 710 includes a memory controller 714,which is operable to perform functions that enable the processor 710 toaccess and communicate with memory 730 that includes a volatile memory732 and/or a non-volatile memory 734. In some embodiments, processor 710is coupled with memory 730 and chipset 720. Processor 710 may also becoupled to a wireless antenna 778 to communicate with any deviceconfigured to transmit and/or receive wireless signals. In oneembodiment, the wireless antenna interface 778 operates in accordancewith, but is not limited to, the IEEE 802.11 standard and its relatedfamily, Home Plug AV (HPAV), Ultra-Wide Band (UWB), Bluetooth, WiMax, orany form of wireless communication protocol.

In some embodiments, volatile memory 732 includes, but is not limitedto, Synchronous Dynamic Random Access Memory (SDRAM), Dynamic RandomAccess Memory (DRAM), RAMBUS Dynamic Random Access Memory (RDRAM),and/or any other type of random access memory device. Non-volatilememory 734 includes, but is not limited to, flash memory, phase changememory (PCM), read-only memory (ROM), electrically erasable programmableread-only memory (EEPROM), or any other type of non-volatile memorydevice.

Memory 730 stores information and instructions to be executed byprocessor 710. In one embodiment, memory 730 may also store temporaryvariables or other intermediate information while processor 710 isexecuting instructions. In the illustrated embodiment, chipset 720connects with processor 710 via Point-to-Point (PtP or P-P) interfaces717 and 722. Chipset 720 enables processor 710 to connect to otherelements in system 700. In some embodiments of the invention, interfaces717 and 722 operate in accordance with a PtP communication protocol suchas the Intel® QuickPath Interconnect (QPI) or the like. In otherembodiments, a different interconnect may be used.

In some embodiments, chipset 720 is operable to communicate withprocessor 710, 705N, display device 740, and other devices 772, 776,774, 760, 762, 764, 766, 777, etc. Buses 750 and 755 may beinterconnected together via a bus bridge 772. Chipset 720 connects toone or more buses 750 and 755 that interconnect various elements 774,760, 762, 764, and 766. Chipset 720 may also be coupled to a wirelessantenna 778 to communicate with any device configured to transmit and/orreceive wireless signals. Chipset 720 connects to display device 740 viainterface (I/F) 726. Display 740 may be, for example, a liquid crystaldisplay (LCD), a plasma display, cathode ray tube (CRT) display, or anyother form of visual display device. In some embodiments of theinvention, processor 710 and chipset 720 are merged into a single SOC.In one embodiment, chipset 720 couples with (e.g., via interface 724) anon-volatile memory 760, a mass storage medium 762, a keyboard/mouse764, and a network interface 766 via I/F 724 and/or I/F 726, I/O devices774, smart TV 776, consumer electronics 777 (e.g., PDA, Smart Phone,Tablet, etc.).

In one embodiment, mass storage medium 762 includes, but is not limitedto, a solid state drive, a hard disk drive, a universal serial bus flashmemory drive, or any other form of computer data storage medium. In oneembodiment, network interface 766 is implemented by any type ofwell-known network interface standard including, but not limited to, anEthernet interface, a universal serial bus (USB) interface, a PeripheralComponent Interconnect (PCI) Express interface, a wireless interfaceand/or any other suitable type of interface. In one embodiment, thewireless interface operates in accordance with, but is not limited to,the IEEE 802.11 standard and its related family, Home Plug AV (HPAV),Ultra-Wide Band (UWB), Bluetooth, WiMax, or any form of wirelesscommunication protocol.

While the modules shown in FIG. 7 are depicted as separate blocks withinthe system 700, the functions performed by some of these blocks may beintegrated within a single semiconductor circuit or may be implementedusing two or more separate integrated circuits. For example, althoughcache memory 716 is depicted as a separate block within processor 710,cache memory 716 (or selected aspects of 716) can be incorporated intoprocessor core 712.

The devices, systems, and methods described can provide improved routingof interconnection between ICs for a multichip package in addition toproviding improved transistor density in the IC die. Examples describedherein include two or three IC dies for simplicity, but one skilled inthe art would recognize upon reading this description that the examplescan include more than three IC dies.

ADDITIONAL DESCRIPTION AND EXAMPLES

Example 1 includes subject matter (such as an electronic device)comprising a first IC die. The IC die includes a first bonding padsurface, and a first backside surface opposite the first bonding padsurface, a first active device layer arranged between the first bondingpad surface and the first backside surface; and at least one stackedthrough silicon via (TSV) disposed between the first backside surfaceand the first bonding pad surface, wherein the at least one stacked TSVincludes a first buried silicon via (BSV) portion having a first widthand a second BSV portion having a second width smaller than the firstwidth, and wherein the first BSV portion extends to the first backsidesurface and the second BSV portion extends to the first active devicelayer.

In Example 2, the subject matter of Example 1 optionally includes apackage substrate and a second IC die. The first backside surface of thefirst IC die is coupled to the package substrate, and the second IC dieincludes a second bonding pad surface and a second backside surfaceopposite the second bonding pad surface, wherein the second IC die isarranged on the first IC die with the second bonding pad surface facingthe first bonding pad surface, and the second BSV portion of the stackedTSV is in electrical contact with the first bonding pad surface of thefirst IC die.

In Example 3, the subject matter of Example 2 optionally includes thesecond IC die including at least one stacked TSV disposed between thesecond backside surface and the second bonding pad surface, wherein theat least one stacked TSV of the second die includes a first BSV portionthat extends to the second backside surface and a second BSV portionthat has a width smaller than a width of the first BSV portion.

In Example 4, the subject matter of one or both of Examples 2 and 3optionally includes a third IC die coupled by solder bumps to the secondbackside surface of the second IC die.

In Example 5, the subject matter of one or any combination of Examples1-4 optionally includes the first IC die including metal layers and vialayers, and the second BSV portion extends through the metal layers andvia layers.

In Example 6, the subject matter of one or any combination of Example1-5 optionally includes the first active device layer includes aplurality of transistors.

In Example 7, the subject matter of one or any combination of Examples1-6 optionally includes a the stacked TSV including a third intermediateBSV portion between the first BSV portion and the second BSV portion,wherein a width of the third BSV portion is smaller than the width ofthe first BSV portion and larger than the width of the second BSVportion.

In Example 8, the subject matter of one or any combination of Examples1-7 optionally includes a second BSV portion of a stacked TSV thatextends through the first active device layer to the first bonding padsurface.

In Example 9, the subject matter of one or any combination of Examples1-8 optionally includes the first bonding pad surface of the first ICdie coupled to the second bonding pad surface of the second IC die usinga plurality of solder bumps.

In Example 10, the subject matter of one or any combination of Examples1-9 optionally includes the first IC die including metal layers and vialayers. The first width of the first BSV portion corresponds to a firstfeature pitch size of the first backside surface, and the second widthcorresponds to a second feature pitch size of one of the first activedevice layer, the metal layers, or the via layers.

In Example 11, the subject matter of one or any combination of Examples1-10 optionally includes the first BSV portion and the second BSVportion each including a substantially rectangular cuboidal shape.

In Example 12, the subject matter of one or any combination of Examples1-10 optionally includes the first BSV portion and the second BSVportion each a substantially cylindrical shape.

In Example 13, the subject matter of one or any combination of Examples1-10 optionally includes the first BSV portion and the second BSVportion both include one of a substantially trapezoidal shape, asubstantially conical shape, or a substantially prismatic shape.

Example 14 includes subject matter (such as a method of forming anelectronic device), or can optionally be combined with one or anycombination of Examples 1-13 to include such subject matter, comprisingforming a first cavity in a backside surface of a first siliconsubstrate, wherein the first portion has a first width; filling thefirst cavity with an electrically conductive material to form a firstburied silicon via (BSV) portion of a stacked through silicon via (TSV);forming a second cavity, wherein the second cavity includes a secondwidth less than the first width; filling the second cavity with theelectrically conductive material to form a second BSV portion of thestacked TSV; electrically connecting the first BSV portion and thesecond BSV portion using one or both of an electroplating process or asolder reflow process; and forming an active device layer in the firstsilicon substrate.

In Example 15, the subject matter of Example 14 optionally includesforming a third cavity prior to forming the second cavity, wherein thethird cavity includes a third width less than the first width andgreater than the second width; and filling the third cavity with theelectrically conductive material to form a third portion of the stackedTSV, wherein the one or both of the electroplating process or the solderreflow process electrically connects the first, second, and third BSVportions of the stacked TSV.

In Example 16, the subject matter of one or both of Examples 14 and 15optionally includes arranging a second silicon substrate on the firstsilicon substrate, wherein the second silicon substrate includes abonding pad surface and a backside surface and at least one stacked TSVdisposed between the backside surface and the bonding pad surface, andthe bonding pad surface of the second silicon substrate is coupled tothe bonding pad surface of the first silicon substrate; and separatingthe first and second silicon substrates into stacked integrated circuit(IC) die.

In Example 17, the subject matter of Example 16 optionally includesarranging a third silicon substrate onto the backside of the secondsilicon substrate, and wherein separating the first and second siliconsubstrates includes separating the first, second, and third siliconsubstrates into stacked IC die.

In Example 18, the subject matter of one or both of Examples 16 and 17optionally includes coupling a backside surface of an IC die of thefirst silicon substrate to a package substrate using solder bumps.

In Example 19, the subject matter of one or any combination of Examples14-18 optionally includes forming the first and second cavities usingone or more of laser drilling, ultra-violet laser drilling, mechanicaldrilling, and etching.

In Example 20, the subject matter of Example 19 optionally includesperforming the one or more of laser drilling, ultra-violet laserdrilling, mechanical drilling, and etching for the second cavity afterthe first portion of the cavity is filled with the electricallyconductive material.

Example 21 includes subject matter (such as an electronic device), orcan optionally be combined with one or any combination of Examples 1-20to include such subject matter, comprising a package substrate, a firstIC die arranged on the package substrate and a second IC die arranged onthe first IC die. The first IC die includes a first bonding pad surfaceand a first backside surface opposite the first bonding pad surface andthe first backside surface coupled to the package substrate; an activedevice layer arranged between the first bonding pad surface and thefirst backside surface, and including a plurality of transistor devices;and at least one stacked through silicon via (TSV) disposed between thefirst backside surface and the first bonding pad surface. The at leastone stacked TSV includes a first buried silicon via (BSV) portion havinga first diameter and a second BSV portion having a second diametersmaller than the first diameter, and the first BSV portion extends tothe first backside surface, and the second BSV portion extends to theactive device layer. The second IC die includes a second bonding padsurface and a second backside surface opposite the second bonding padsurface, wherein the second bonding pad surface is coupled to the firstbonding pad surface.

In Example 22, the subject matter of Example 21 optionally includes athird IC die arranged on the second IC die and coupled to the secondbackside surface, wherein the second IC die includes at least onestacked TSV disposed between the second backside surface and the secondbonding pad surface, wherein the at least one stacked TSV of the seconddie includes a first BSV portion that extends to the second backsidesurface and a second BSV portion that has a diameter smaller than adiameter of the first BSV portion.

In Example 23, the subject matter of one or both of Examples 21 and 22optionally includes the stacked TSV of the first IC die extending fromthe first backside surface through the active device layer to the firstbonding pad surface.

These non-limiting examples can be combined in any permutation orcombination. The Abstract is provided to allow the reader to ascertainthe nature and gist of the technical disclosure. It is submitted withthe understanding that it will not be used to limit or interpret thescope or meaning of the claims. The following claims are herebyincorporated into the detailed description, with each claim standing onits own as a separate embodiment.

What is claimed is:
 1. An electronic device comprising a firstintegrated circuit (IC) die, the first IC die including: a first bondingpad surface, and a first backside surface opposite the first bonding padsurface; a first active device layer arranged between the first bondingpad surface and the first backside surface; and at least one stackedthrough silicon via (TSV) disposed between the first backside surfaceand the first bonding pad surface, wherein the at least one stacked TSVincludes a first buried silicon via (BSV) portion having a first width,a second BSV portion having a second width smaller than the first width,and a third intermediate BSV portion between the first BSV portion andthe second BSV portion, wherein a width of the third BSV portion issmaller than the width of the first BSV portion and larger than thewidth of the second BSV portion, and wherein the first BSV portionextends to the first backside surface and the second BSV portion extendsat least to the first active device layer.
 2. The electronic device ofclaim 1, including: a package substrate, wherein the first backsidesurface of the first IC die is coupled to the package substrate; and asecond IC die including a second bonding pad surface and a secondbackside surface opposite the second bonding pad surface, wherein thesecond IC die is arranged on the first IC die with the second bondingpad surface facing the first bonding pad surface, and the second BSVportion of the stacked TSV is in electrical contact with the firstbonding pad surface of the first IC die.
 3. The electronic device ofclaim 2, wherein the second IC die includes at least one stacked TSVdisposed between the second backside surface and the second bonding padsurface, wherein the at least one stacked TSV of the second die includesa first BSV portion that extends to the second backside surface and asecond BSV portion that has a width smaller than a width of the firstBSV portion.
 4. The electronic device of claim 2, including a third ICdie coupled by solder bumps to the second backside surface of the secondIC die.
 5. The electronic device of claim 1, wherein the first IC dieincludes metal layers and via layers, and the second BSV portion extendsthrough the metal layers and via layers.
 6. The electronic device ofclaim 1, wherein the first active device layer includes a plurality oftransistors.
 7. The electronic device of claim 1, wherein the second BSVportion extends through the first active device layer to the firstbonding pad surface.
 8. The electronic device of claim 1, wherein thefirst bonding pad surface of the first IC die is coupled to the secondbonding pad surface of the second IC die using a plurality of solderbumps.
 9. The electronic device of claim 1, wherein the first IC dieincludes metal layers and via layers; and wherein the first widthcorresponds to a first feature pitch size of the first backside surface,and the second width corresponds to a second feature pitch size of oneof the first active device layer, the metal layers, or the via layers.10. The electronic device of claim 1, wherein the first BSV portion andthe second BSV portion each include a substantially rectangular cuboidalshape.
 11. The electronic device of claim 1, wherein the first BSVportion and the second BSV portion each a substantially cylindricalshape.
 12. The electronic device of claim 1, wherein the first BSVportion and the second BSV portion both include one of a substantiallytrapezoidal shape, a substantially conical shape, or a substantiallyprismatic shape.
 13. A method of forming an electronic device, themethod comprising: forming a first cavity in a backside surface of afirst silicon substrate, wherein the first portion has a first width;filling the first cavity with an electrically conductive material toform a first buried silicon via (BSV) portion of a stacked throughsilicon via (TSV); forming a second cavity, wherein the second cavityincludes a second width less than the first width; filling the secondcavity with the electrically conductive material to form a second BSVportion of the stacked TSV; electrically connecting the first BSVportion and the second BSV portion using one or both of anelectroplating process or a solder reflow process; and forming an activedevice layer in the first silicon substrate.
 14. The method of claim 13,including: forming a third cavity prior to forming the second cavity,wherein the third cavity includes a third width less than the firstwidth and greater than the second width; and filling the third cavitywith the electrically conductive material to form a third portion of thestacked TSV, wherein the one or both of the electroplating process orthe solder reflow process electrically connects the first, second, andthird BSV portions of the stacked TSV.
 15. The method of claim 13,wherein the method further includes: arranging a second siliconsubstrate on the first silicon substrate, wherein the second siliconsubstrate includes a bonding pad surface and a backside surface and atleast one stacked TSV disposed between the backside surface and thebonding pad surface, and the bonding pad surface of the second siliconsubstrate is coupled to the bonding pad surface of the first siliconsubstrate; and separating the first and second silicon substrates intostacked integrated circuit (IC) die.
 16. The method of claim 15,including arranging a third silicon substrate onto the backside of thesecond silicon substrate, and wherein separating the first and secondsilicon substrates includes separating the first, second, and thirdsilicon substrates into stacked IC die.
 17. The method of claim 15,including coupling a backside surface of an IC die of the first siliconsubstrate to a package substrate using solder bumps.
 18. The method ofclaim 13, wherein forming the first and second cavities includes one ormore of laser drilling, ultra-violet laser drilling, mechanicaldrilling, and etching.
 19. The method of claim 18, wherein the one ormore of laser drilling, ultra-violet laser drilling, mechanicaldrilling, and etching for the second cavity is performed after the firstportion of the cavity is filled with the electrically conductivematerial.
 20. An electronic device comprising: a package substrate; afirst integrated circuit (IC) die arranged on the package substrate, thefirst IC die including: a first bonding pad surface and a first backsidesurface opposite the first bonding pad surface and the first backsidesurface coupled to the package substrate; an active device layerarranged between the first bonding pad surface and the first backsidesurface, and including a plurality of transistor devices; and at leastone stacked through silicon via (TSV) disposed between the firstbackside surface and the first bonding pad surface, wherein the at leastone stacked TSV includes a first buried silicon via (BSV) portion havinga first diameter and a second BSV portion having a second diametersmaller than the first diameter, and the first BSV portion and thesecond BSV portion each include a substantially rectangular cuboidalshape or each include a substantially cylindrical shape; wherein thefirst BSV portion extends to the first backside surface, and the secondBSV portion extends to the active device layer; and a second IC diearranged on the first IC die and including a second bonding pad surfaceand a second backside surface opposite the second bonding pad surface,wherein the second bonding pad surface is coupled to the first bondingpad surface.
 21. The electronic device of claim 20, including a third ICdie arranged on the second IC die and coupled to the second backsidesurface, wherein the second IC die includes at least one stacked TSVdisposed between the second backside surface and the second bonding padsurface, wherein the at least one stacked TSV of the second die includesa first BSV portion that extends to the second backside surface and asecond BSV portion that has a diameter smaller than a diameter of thefirst BSV portion.
 22. The electronic device of claim 20, wherein thestacked TSV of the first IC die extends from the first backside surfacethrough the active device layer to the first bonding pad surface.